Implantable medical leads can be used to deliver electrical stimulation to the body tissue through implantable medical devices. Exemplary implantable devices include cardiac rhythm management (CRM) systems (e.g., pacemakers, defibrillators, and cardiac resynchronization therapy devices) and neurostimulation systems (e.g., spinal cord stimulation (SCS) systems). For CRM systems, the medical leads typically extend intravascularly to an implant location within or on a patient's heart. The implantable medical leads can be equipped with at least one electrode. The implantable medical leads are often positioned so that the electrode delivers electrical stimulation to a target tissue without stimulating adjacent tissue. The implantable medical leads can be flexible and can require use of a support device (e.g., a stylet) to effectively guide the implantable medical lead into a desired location inside the heart of a patient. A stylet-driven implantable medical lead can have a pre-formed shape to facilitate advancement of the medical lead to certain locations within the heart.
Implantable medical leads are often anchored or fixed to heart tissue using an active (i.e., movable or deployable) fixation anchor, such as a rotatable helix, located at or near a distal end of the lead. As the medical leads are typically flexible in torsion, it can be a challenge to use the lead body to rotate the helix. For stylet-driven implantable medical leads, the stylet can operate to deliver torque from a proximal end of the lead to an active fixation mechanism at or near the distal end of the lead.